shades

Simple Colour Manipulation

The shades package allows colours to be manipulated easily in R. Properties such as brightness and saturation can be quickly queried, changed or varied, and perceptually uniform colour gradients can be constructed. It plays nicely with the pipe operator from the popular magrittr package, and fits naturally into that paradigm. It can also be used with ggplot2 scales.

The package is available on CRAN. You can also install the current development version from GitHub using devtools:

# install.packages("devtools")

devtools::install_github("jonclayden/shades")

Feedback on the package or suggestions are welcome, either by filing an issue or by email.

Usage

Colours are represented in R using CSS-style hex strings, but there is also a dictionary of predefined named colours such as "red" and "blue". Either of these may be passed to most graphics functions, but creating variations on a particular colour can be awkward.

The shades package defines a simple class, shade, which uses exactly this same convention and is entirely compatible with built-in colours, but it also stores information about the coordinates of the colours in a particular colour space.

library(shades)

red <- shade("red")

print(unclass(red))

## [1] "red"

## attr(,"space")

## [1] "sRGB"

## attr(,"coords")

## R G B

## [1,] 1 0 0

From here, the package switches between colour spaces as required, allowing various kinds of colour manipulation to be performed straightforwardly. For example, let's find the saturation level of a few built-in colours.

saturation(c("papayawhip","lavenderblush","olivedrab"))

## [1] 0.1647100 0.0588200 0.7535287

Now let's consider a colour gradient stepping through two different colour spaces, which we might want to use as a palette or colour scale.

swatch(gradient(c("red","blue"), 5))

swatch(gradient(c("red","blue"), 5, space="Lab"))

Here, we are using the swatch function to visualise a set of colours as a series of squares. Notice the more uniform appearance of the gradient when it traverses through the Lab colour space.

Similarly, we can create a set of new colours by changing the brightness and saturation levels of some base colours, and make the code more readable by using the magrittr pipe operator.

This operation takes the original two colours, reduces their brightness to 60%, assigns a whole series of saturation levels to the result, and then passes it to swatch for visualisation. Notice that the pipeline is combinative (like the base function outer), returning each combination of parameters in a multidimensional array. The final shades are arranged in two rows by swatch, for convenience.

Any of these gradients can be directly passed to a standard graphical function, to be used as a colour scale. However, when choosing a colour scale, it is helpful to bear in mind that some viewers may have a colour vision deficiency (colour blindness), making it harder for them to distinguish certain colours and therefore to see a continuous scale. The dichromat function can be used to simulate this.

rev(grDevices::rainbow(9)) %>% dichromat %>% swatch

gradient("viridis",9) %>% dichromat %>% swatch

Here we are using the built-in "viridis" colour map, developed for Python's matplotlib, which was specifically designed to appear continuous under as many conditions as possible. When shown with simulated red-blindness, the default for dichromat, it is clearly much more interpretable than a typical rainbow palette generated by R's built-in graphics functions.

The package also supports colour mixing, either additively (as with light) or subtractively (as with paint). For example, consider additive mixtures of the three primary RGB colours.

A "light mixture" infix operator, %.)%, and a "paint mixture" infix operator, %_/%, are also available.

("red" %.)% "green") == "yellow"

## [1] TRUE

("cyan" %_/% "magenta") == "blue"

## [1] TRUE

Finally, you can calculate perceptual distances to a reference colour, as in

distance(c("red","green","blue"), "red")

## [1] 0.00000 86.52385 53.07649

Interoperability with ggplot2

The shades package can be used with the popular ggplot2 graphics library in different ways, with different levels of integration. Firstly, gradients from this package can be used as ggplot2 colour scales through the manual scale functions; for example,

This does not require the two packages to know anything about each other, and is flexible and powerful, but it doesn't easily allow existing ggplot2 scales to be modified using the colour manipulation functions from shades. As of shades version 1.3.0, it is also possible to call the package's colour property functions directly on palette functions and scales, so that (for example), we can darken all colours in an existing scale slightly:

Notice here that we have chosen to use the delta() function, which is available in all colour property functions, to request a relative reduction of 20 to the original lightness of each colour in the scale. We could also have given a literal value to fix the lightness of all colours to a certain level.

Related packages

The shades package aims to bring together a range of colour manipulation tools and make them easy to use. However, there are several other packages available that can do similar things, sometimes in slightly different ways. These include

the grDevices package, which is shipped with R and used as the basis for shades;

the venerable colorspace package, which provides formal colour classes and transformations between spaces;

munsell, which interprets colours in Munsell notation and does some colour manipulation;

It is now possible to manipulate palette functions and ggplot2 scales using
the colour manipulation functions in this package (#5, #7). When passed one
of these objects, a modified wrapper object is returned. This allows colour
tweaks to be made to standard scales in ggplot2 plots. See the README for a
visual example.

The gradient() function now returns a function if its second argument is
missing or NULL. This change is complementary to the one above, allowing
palette functions to be created.

There is now support for transparency, which can be queried or modified
through the new opacity() function, which functions just like the other
colour property functions (#4). Opacity (alpha) values are stored as an
attribute with shade objects, and reflected in the RGB hex representation
only when less than 1.

The scalefac() functional has been added, which multiplies its argument just
as delta() adds it. Both functions now accept, and concatenate, multiple
arguments for convenience.

The usual behaviour of the colour property manipulation functions, which
vectorise over both arguments, can be suppressed by wrapping replacement
values with the recycle() function, which reverts to a standard R
"recycling" scheme with final dimensions matching the original.

The dichromat() function now offers a pass-through (normal colour vision)
option, and is also vectorised over its second argument (#3). Some of the
coefficients it uses internally are now pre-calculated and cached for
efficiency.

There is now a print method for vectors of class shade.

An empty shade vector is now explicitly an error.

The README now includes an example of using shades with ggplot2 (#2), as
well as links to several related packages.

Support for two new colour spaces has been added: LMS, a direct
representation of the response levels of each of the three colour receptor
types in the eye; and LCh, a polar representation of Lab space.

The new dichromat() function can be used to simulate colour blindness.

The gradient() function now additionally supports predefined colour maps from
matplotlib and ColorBrewer. Its second argument is now interpreted a little
differently.

The hueshift() function has been removed, in favour of the more general
combination of hue() and delta(). hue(x, delta(y)) is the equivalent of the
old hueshift(x,y), and delta() can also be used with other colour properties.

New colour property functions lightness() and chroma() have been added.

Dimensions are now set when two or more colour properties are changed, and
the swatch() visualisation function plots multidimensional shades in a grid.

There is now a rev() method for shades.

The all.equal() method for shades now passes on its ellipsis argument when
checking colour coordinates.

The package has been reworked to use functions from base R to warp colour
coordinates between spaces and so on. It therefore no longer depends on the
"colorspace" package, but the list of supported colour spaces has changed
somewhat as a result.